The present invention relates to surgical apparatus for the localized treatment of tissue by the application of light energy, and particularly to the area of laser surgery wherein tissue is cut, cauterized or otherwise subjected to laser light.
In such system there is a complicated set of design constraints imposed, on the one hand, by the available systems for generating laser light at particular wavelengths and powers suitable for different surgical applications, and, on the other hand, by the characteristics of probes or instruments for delivering the light to a surgical site and applying it to cut, coagulate or otherwise treat or analyze tissue.
In broad terms, the efficiency with which light of a given wavelength is absorbed by a particular tissue determines its depth of penetration, and thus the degree to which a pulse of such light will primarily cause either a superficial cutting action and tissue ablation without heat transfer to underlying tissue, or will cause a heating action to a depth effective to cauterize tissue. Both of these actions are generally desired for surgical purposes, thus requiring light of two substantially different wavelengths, at relatively high average power levels. In addition, light of different wavelength at lower powers may also be desirable for visualization or certain forms of analysis, particularly in surgical arenas where the light is applied by endoscopic instrument.
The probes or instruments for delivering such light to a tissue site must guide the light with minimal losses from the laser source, and minimal parasitic heat generation. Two basic structures have evolved to achieve this purpose. In one, a highly reflective metallic tube structure, fabricated as an articulated arm, guides light by internal reflection to a probe end which is aimed at the tissue. In the other, fiber optics serve as the light guide, allowing greater flexibility in the delivery of light to, and manipulation of, the surgical probe. Hybrid delivery systems are also possible, although for particular wavelength bands absorption by the fiber may preclude the use of the fiber optic approach.
These constraints have meant, in practice, that a multi-wavelength surgical apparatus requires several distinct laser light sources, With precision alignment and coupling of the different sources into a common waveguide or probe structure, and the provision of a number of different controls to select working wavelength and set the desired power. These factors affect the production cost, the field reliability and the ease of use of such systems.